1. Field of the Invention
Aspects of the present invention relate to a negative electrode active material and a secondary battery including the same.
2. Description of the Related Art
Research into secondary batteries is currently being conducted, with an emphasis towards producing a secondary battery that is ultra-light weight, has a high-energy density, a high-output voltage, a low self-discharge rate, is environmentally friendly, and has a long lifespan. A secondary battery may be broadly classified as a nickel-hydrogen (Ni-MH) battery or a lithium ion (Li-ion) battery, depending on the type of electrode active material included therein. Particularly, a lithium ion battery may be categorized according to the type of electrolyte included therein, e.g., a liquid electrolyte, a solid polymer electrolyte, or a gel-like electrolyte. Further, a secondary battery may be further classified according to the type of container that houses an electrode assembly, such as a can-type, a pouch-type, and the like
A lithium ion battery has a higher energy density per unit weight and a higher average voltage (3.6V/cell) than other types of secondary batteries, such as a NiCad battery and a nickel/hydrogen battery, which have an average voltage of 1.2V. Further, a lithium ion battery exhibits a variety of advantages, such as a self-discharge rate of less than 5% per month, at 20° C., which is about ⅓ the self-discharge rate of a NiCad battery or a nickel/hydrogen battery. In addition, lithium ion batteries are environmentally friendly, as they do not include heavy metals, such as cadmium (Cd) and mercury (Hg), and are capable of being charged and discharged more than 1000 times, under normal operation conditions. Recent advancements of information and communication technologies have provided a strong demand for the rapid development of improved lithium ion batteries.
Generally, a secondary battery is fabricated by placing an electrode assembly, composed of a positive electrode plate, a negative electrode plate, and a separator disposed therebetween, and an electrolyte, in a can made of aluminum or an aluminum alloy. An opening of the can is then sealed with a cap assembly.
Each of the positive electrode plate and negative electrode plate includes a positive electrode active material and a negative electrode active material, which are capable of reversibly intercalating lithium ions. The positive electrode active material can include lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, or the like.
The lithium nickel oxide generally has a low content of cobalt and therefore, is less susceptible to the fluctuation in the price of cobalt, as compared to the lithium cobalt oxide. In addition, lithium nickel oxide is more economical, due to having a high manganese content. To this end, a great deal of research has been actively focused on developing a positive electrode active material that includes a lithium nickel oxide compound.
However, lithium nickel oxide exhibits poor initial charge/discharge efficiency, and therefore, suffers from a large initial irreversible capacity. This results in a need for a comparatively larger amount of the negative electrode active material, leading to a reduction in battery capacity.